It has been shown that several different types of peripheral lesions including transection and regeneration of peripheral nerves, are capable of eliciting significant organizational changes in primate somatosensory cortex. It has been suggested that these organizational changes may parallel in some manner the clinically observed recovery from sensory deficits experienced following traumatic injury to peripheral nerves. In the proposed research, we will employ the procedure we recently developed to examine the effects of impulses in individual primary sensory afferents on identified dorsal horn neurons. This procedure consists of: 1) Establishing a stable intracellular recording in a characterized primary sensory afferent in the dorsal root ganglion; 2) locating an identified dorsal horn interneuron with a receptive field which contains that of the primary afferent; 3) Intracellularly stimulating the afferent while simultaneously recording, either extracellularly or intracellularly, the response of the dorsal horn interneuron. The long term objectives of the proposed research are: 1) Determine how specific sensory inputs from individual characterized primary sensory afferents are processed by identified and characterized dorsal horn interneurons, including both cells of origin of specific ascending systems and cells involved in propriospinal pathways; 2) Examine the effects of peripheral nerve transection and regeneration on the processing of these specific inputs over time, initially when regenerating fibers first reach the skin and reinnervate cutaneous receptors in some preparations and several months after recovery in others; 3) Evaluate the plastic capabilities in the central processing of these precise inputs during this recovery period; 4) Determine to what extent (if at all) this plasticity in the spinal dorsal horn may subserve the observed organizational changes in the somatosensory cortex.